After stratifying for previous use of TMP/SMX and/or IVIG, subjects will be randomized to one of two arms, TMP/SMX 5 mg/kg/day dose or micronized atovaquone, 30mg/kg/day dose plus azithromycin 5mg/kg/day dose. Subjects will be evaluated for safety and tolerance of the study drugs. Subjects will also be tested for equivalence of antibacterial agents by the monitoring for occurrence of serious bacterial infections or PCP breakthrough.